Three mail bombs have exploded in Austin in the past two weeks, killing two and injuring two others.

In the aftermath of the bombings, law enforcement has reported 150 calls from residents scared that their mail might be explosive, and police are asking anyone who receives a suspicious package to call authorities immediately.

"What caused this in these instances was a suspicious package that no one was suspecting or expecting," Austin Mayor Steve Adler told CNN Tuesday. "I want everyone in my community, if they see something that's suspicious—a package or otherwise—I want them to pick up the phone and call 911."

On Monday, a mail bomb killed a 17-year-old black student. The first victim, Anthony Stephan House, was killed on March 2. Both victims were prominent members of Austin's African-American community, according to the Washington Post, and House was the stepson of Freddie Dixon, the former pastor of a historic black church. A third victim, who was injured in a separate blast on Monday, was described by police as a "75-year-old Hispanic woman."

While police have not released a suspect's name or formulated a motive, Dixon told the Washington Post he believes the bombings are connected, as the 17-year-old was the grandson of Dixon's longtime friend, Norman Mason. “Are you trying to say something to prominent African American families?” Dixon told the Post. “I don’t know who they’ve been targeting, but for sure, they went and got one of my best friend’s grandson. Somebody knew the connection...

“My diagnosis: Number one, I think it’s a hate crime. Number two, somebody’s got some kind of vendetta here.”